It is a fundamental precept of vehicular travel that efficiency of the vehicle increases as negative aerodynamic forces exerted upon the vehicle during its travel decrease. For example, with aircraft, lift must exceed the weight of the aircraft, and propulsive thrust must exceed the drag upon the craft, in order for the airplane to even minimally function.
In the case of land vehicles, lift and weight vectors do not come into the picture other than to the extent that the weight of the vehicle bears upon horizontal components of frictional forces exerted upon the vehicle by the ground over which it is traveling. Essentially, however, the question is one of resolution of a propulsive thrust/drag model.
In a still atmosphere, when a land vehicle is starting, the question is merely one of propulsive thrust overcoming a drag force created by friction between the vehicle and the land surface. In the typical case, this is easily accomplished.
As the vehicle begins to move, however, relative wind becomes exerted upon vertical and oblique surfaces of the body of the vehicle. The system becomes further exaggerated if a vehicle is traveling in an environment where ambient wind conditions exist. Under such circumstances, the drag component normally present because of friction is additive with that created by both relative wind induced by movement of the vehicle and, when the true wind is in a direction opposite the direction of movement of the vehicle, the true wind.
Pickup trucks are vehicles which present unique problems with regard to the principles previously discussed herein. The typical pickup truck includes a storage compartment comprising an open storage bed. During movement of such a vehicle on a highway, for example, there is a tendency for the airstream to flow over the cab, downwardly into the bed, and, thereafter, through the bed and against the tailgate or a rear wall of the bed. Not only does such flow tend to blow contents carried within the truck out of the bed, but it acts as a retarding force.
Pickup trucks commercially purchasable are provided with sufficient horsepower to overcome the various drag forces exerted thereon during typical circumstances. Only in the utmost extreme wind conditions might operation of the vehicle prove impossible.
Nevertheless, owners and operators of pickup trucks need be concerned about other factors. The retarding force exerted upon the tailgate of such a truck is adversely reflected in the lowered gasoline mileage which can be obtained. During one test conducted, it was determined that the force exerted upon a pickup truck tailgate while traveling at 55 miles per hour was 1.5 pounds per unit area. As can be seen, the total force exerted upon the vehicle as a result of various wind vectors acting upon the tailgate can be substantial. Such negative aerodynamic forces can significantly decrease the gasoline mileage obtained by the vehicle.
Various solutions have been attempted in order to solve these problems. One measure that owners and operators of pickup trucks have utilized is removal of the surface which can be encountered by the wind force by lowering the tailgate during operation of the vehicle. By taking such action, the airstream is allowed to pass through the truck bed and out thereof without encountering any obstacle.
Such a solution certainly has drawbacks. Most pickup trucks do not provide means for securing the tailgate in a down position. As a result, as the vehicle moves over a road surface and encounters bumps and other irregularities in the road, the tailgate will "bounce" and can be damaged. Additionally, if something might be being carried in the bed of the truck which might not, of itself, induce a significant drag, the tailgate in a down position might permit the cargo to fall out of the vehicle and onto the road. Not only may the cargo be damaged, but significant hazards might be presented to other drivers.
Another attempted solution is one illustrated in U.S. Pat. No. 4,072,336 which was issued to Leo J. Ruzicka on Feb. 7, 1978 for a device entitled VACUUM SPOILER FOR PICKUP. The device of that patent would provide for the provision of a slot cut through the front portions of the pickup truck bed. The slot would extend laterally with regard to the direction of movement of the vehicle. Air flow passing upwardly through the slot at high speeds would tend to spoil a vacuum created behind the cab of the vehicle. The theory of the Ruzicka structure is that, as a result of the vacuum reduction, better gas mileage can be achieved.
A structure in accordance with the Ruzicka patent does, however, still have certain disadvantages. Because of the air flow over the cab and down into the bed, a reduced pressure would be created in the bed, and air coming from below the vehicle could be sucked up through the slot at a very high velocity. As a result, any cargo carried ip the bed of the truck might become dislodged or even thrown out of the vehicle. Additionally, even with the vacuum reduction behind the cab, some air flow will still impinge upon the tailgate, and additional drag will be created.
Other attempted solutions have sought to divert air flow over the cab upwardly so that it will not confront the tailgate. Such a structure is illustrated in U.S. Pat. No. 4,159,853 (Crossman). That patent issued on July 3, 1979 upon an application filed on Sept. 28, 1977. The device of that patent is entitled PICKUP TRUCK AIR DEFLECTOR. The structure essentially comprises an airfoil for merely diverting air flow in a direction upwardly. The theory of operation of the structure is that flux lines of the air flow will be displaced sufficiently so that little, if any, air flow is brought to bear upon the tailgate. Still, however, while there may be some reduction of the drag created by impingement of the air flow upon the tailgate, there will be some pressure exerted against that structure.
U.S. Pat. No. 4,451,075 (Canfield) illustrates another type of structure designed to solve the problems of the prior art. The structure of the Canfield patent is somewhat akin to the present invention. It provides a sloping backwall positionable in the rear portions of the bed of a pickup truck in order to provide an airfoil, whereby wind resistance caused by engagement of the tailgate by the wind is reduced to commensurately increase gasoline mileage. Additionally, the sloping wall, in combination with the tailgate, functions to provide a compartment which can be used as a tool box or other storage compartment.
As with other solutions which have been attempted, however, the structure of the Canfield patent has certain drawbacks. While the sloping wall may very efficiently function to reduce the drag exerted upon the vehicle in which it is installed, it virtually becomes a permanent fixture of the truck. If the owner of the truck purchases a device in accordance with the Canfield patent, and subsequently purchases another truck whose bed has different dimensions, the structure in accordance with Canfield cannot be removed and installed in the newer vehicle. Even if it could, however, the older truck may prove less saleable because of holes which need to be drilled into the truck wheel wells and interior side walls of the truck bed. Similarly, even if the truck owner does not sell a vehicle in which the Canfield structure is installed, but, rather, wishes to remove the improvised tool box in order to increase hauling capacity of the vehicle, the drilled holes are present and can be acted upon by the environment to accelerate corrosion and deterioration.
The present invention is an improved air deflector which goes far to solve the problems of the prior art. It is designed specifically for use with pickup trucks, but it can be used with such trucks having beds with virtually any dimension currently available commercially. Additionally, it need not be permanently affixed to the vehicle in a way so that damage would be inflicted thereupon.